The present invention relates to a process for the preparation of iron nitrosyl carbonyl, more particularly to an improvement in that process.
The complex iron nitrosyl carbonyl [Fe(NO).sub.2 (CO).sub.2 ], is known to dimerize butadiene to produce vinyl cyclohexene (VCH). Methods known to prepare various iron nitrosyl complexes require reduction of [Fe(NO).sub.2 Cl].sub.2 or reaction of nitric oxide (NO) on a mixture of iron and FeCl.sub.3. Reference to these methods is found in U.S. Pat. No.4,238,301. Another patent, U.S. Pat. No. 4,234,454, discloses the preparation of various metal nitrosyl catalytic solutions by employing the combination of manganese, zinc or tin together with iron, cobalt or nickel nitrosyl halides to produce the respective metal nitrosyls in a system for dimerizing various conjugated dienes. An earlier patent, U.S. Pat. No. 3,510,533, discloses the dimerization of conjugated dienes with .pi.-allyldinitrosyliron complexes and a method for their preparation. Several methods are given involving the reduction of a .mu.,.mu.'-dihalotetranitrosyldiiron. Additionally, iron nitrosyl carbonyl is prepared by a process of reducing iron, cobalt or nickel chlorides and an alkali metal nitrite or iron, cobalt or nickel nitrosyl chlorides with carbon monoxide (CO) in the presence of a readily oxidizable metal as taught in copending U.S. application Ser. No. 07,348,625 filed May 8, 1989 (Heaton).
These methods produce a product which admits of further purification. Purification, such as distillation, usually involves vaporizing the iron nitrosyl carbonyl using heat and trapping the product, e.g. using dry ice or dry ice and acetone. Such purifications are disadvantageous in that they involve heat which may decompose product and involve additional steps and equipment which can result in loss of product. Other disadvantages include need for large scale cryogenic equipment to trap product.
It would be desirable to purify iron nitrosyl carbonyl without use of additional heat and preferably as part of the preparation of the material rather than in a separate process.